1. Field of the Invention
The present invention relates to an image transmitting system that has an image transmitting device that transmits image data by means of wireless communication that uses a wireless communication format such as wireless LAN or the like, and an image receiving device that receives image data by means of wireless communication.
Priority is claimed on Japanese Patent Application No. 2009-243291, filed Oct. 22, 2009, the content of which is incorporated herein by reference.
2. Description of Related Art
In recent years, endoscope devices have come to be widely used that, by inserting a long narrow insertion unit into a body cavity or conduit, can observe with a monitor a subject image of the body cavity or conduit. This kind of endoscope device generally has an endoscope that has an insertion unit that is inserted in a body cavity or conduit, and a main body device that has a light source device and video processor. This endoscope and main body device are connected by a light guide cable that guides illumination light from the light source device to the endoscope, and a signal cable that transmits the image signal obtained by the endoscope to the video processor. Thereby, the range of movement of the endoscope was restricted and the operability of the endoscope was hindered.
Therefore, for example, in Japanese Unexamined Patent Application, First Publication S60-48011 (hereinbelow, referred to as Patent Document 1), an illumination device constituted by an LED (light-emitting diode) or the like is built into the endoscope. With this constitution, the light guide cable that extends from the endoscope is removed. Also, the endoscope is provided with a video signal processing circuit that obtains a video signal that can be shown on a monitor by performing a video signal process on the image signal, and a transmitting circuit that transmits this video signal via radio. Separately from the endoscope, a receiving device that receives the radio waves and demodulates the video signal is provided. With this constitution, the signal cable that extends from the endoscope is removed. This type of endoscope device is generally called a wireless endoscope device, and it has the advantages of the restrictions in the range of movement of the endoscope being eased, and the operability improving.
In the conventional wireless endoscope device, the receiving device is provided separately from the endoscope. Due to having such a structure, it is necessary to perform setting of the communication channel of the endoscope on the transmission side in accordance with the communication channel that is set in the receiving device, and to make a connection by wireless communication. A method is also conceivable of uniquely determining a combination of receiving device and endoscope, and setting the communication channel thereof in a fixed manner to an arbitrary channel in advance. However, in a hospital, a plurality of receiving devices and a plurality of endoscopes are used, and the disinfection/sterilization treatment of endoscopes and inspection are carried out simultaneously. For this reason, combinations of a receiving device and an endoscope are not uniquely determined Also, in order to prevent radio wave interference, the communication channels of the receiving devices need to be set to respectively differ.
As the communication method that is used for wireless communication, it is effective to use a wireless communication method such as IEEE 802.11 that is used in wireless LANs in which high-speed data communication is possible. In this wireless communication method, in order to effectively use the frequency band, wireless communication can be performed by selecting an arbitrary channel from a plurality of channels. Each of the communication channels is arranged so that the usable frequency band partially overlaps with another communication channel as shown in FIG. 13, due to restrictions of the available frequency band. For this reason, at the start of operation, the endoscope device checks the status of use of available communication channels to determine the optimal communication channel, and starts wireless communication between the receiving device and the endoscope.
Generally, in data communication of a communication channel that is set to a wireless terminal, transmission control of data is performed by CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). FIG. 14 shows the communication sequence of this method. When transmitting a transmission frame, a wireless terminal A confirms the usage state of communication channel CHa. As a result, when the communication channel CHa is determined to be in use (busy state), processing is performed to avoid a collision of transmission frames by stopping the transmission of transmission frames until the wireless terminal B that is performing the current frame transmission completes the transmission.
For this reason, in the case of the usage state of communication channels determined at the start of communication changing during data communication, such as a rapid increase in the amount of data communication of another wireless terminal due to the start of file transmission by a PC or the like, there may have been an influence on the transmission, such as the probability of a busy state of the communication channel occurring increasing, and the transmission rate falling. In contrast to this, Japanese Unexamined Patent Application, First Publication 2006-109448 (hereinbelow referred to as Patent Document 2) provides a wireless LAN system that calculates a receiving rate of frames including another BSSID different from a corresponding BSSID among the whole received frames, detects whether or not interference takes place between the BSSs on the basis of the this receiving rate, and changes the communication channel.